1. Technical Field of the Invention
The present invention relates to the formulation of effective amounts of at least one polyholoside into cosmetic/pharmaceutical/dermatological compositions, in particular for topical application, to promote the desquamation of the skin and/or to stimulate epidermal renewal and/or to combat aging of the skin.
This invention also relates to a regimen or treatment for promoting the desquamation of the skin and/or stimulating epidermal renewal and thus combating intrinsic and/or extrinsic aging of the skin.
2. Description of the Prior Art
Desquamation is a natural phenomenon associated with the fact that the epidermis, which constitutes the upper layer of the skin, is in constant regeneration. The epidermis consists of several layers of cells, the deepest of which is the basal layer consisting of undifferentiated cells. These cells differentiate and migrate towards the surface of the epidermis over time, traversing the various layers thereof, until they form, at the surface of the epidermis, the corneocytes which are dead cells which are removed by desquamation. This loss of surface is compensated for by the migration of cells from the basal layer to the surface of the epidermis. This amounts to perpetual renewal of the skin. Forced removal of the horny layer accelerates the renewal and makes it possible to effectively combat aging.
At the same time, these cells continue their differentiation, the final stage of which is the formation of corneocytes. These are dead cells which constitute the final layer of the epidermis, namely, the outermost layer also known as the stratum corneum.
Aging of the skin resulting from the effects of intrinsic or extrinsic factors on the skin is reflected by the appearance of wrinkles and fine lines, by yellowing of the skin which develops a parchment-like appearance accompanied by the appearance of pigmentation blemishes, by disorganization of the elastin and collagen fibers, promoting a loss of elasticity, flexibility and firmness, and by the appearance of telangiectasias.
Certain of these signs of aging are more particularly associated with intrinsic or physiological aging, i.e., "normal" aging due to age or chronobiological aging, whereas others are more specific for extrinsic aging, i.e., aging caused by the environment in general; this relates more particularly to photoaging due to exposure to sunlight, to light or to any other radiation.
The invention described below concerns intrinsic or physiological aging, as well as extrinsic aging.
The changes in the skin due to intrinsic aging are the consequence of a genetically programmed senescence involving endogenous factors. This intrinsic aging results, in particular, in a slowing of the renewal of the skin cells, which is reflected essentially by the appearance of clinical impairments, such as reduction in the subcutaneous adipose tissue and the appearance of small wrinkles or fine lines, and by histopathological changes such as an increase in the number and thickness of elastic fibers, a loss of vertical fibers from the membrane of the elastic tissue, and the presence of large irregular fibroblasts in the cells of this elastic tissue.
In contrast, extrinsic aging promotes clinical impairments such as large wrinkles and the formation of a flaccid and tanned skin, and histopathological changes such as excessive accumulation of elastic materials in the epidermis and degeneration of the collagen fibers.
Various active agents for combating aging of the skin are known to this art.
Thus, U.S. Pat. No. 4,603,146 describes the use of retinoic acid and derivatives thereof in cosmetic compositions in order to combat aging of the skin.
Too, many patents and publications (see for example, EP-A-413,528) describe the use of, and many commercial cosmetic compositions contain, .alpha.-hydroxy acids such as lactic acid, glycolic acid or citric acid for combating aging of the skin.
Lastly, beta-hydroxy acids and, more especially, salicyclic acid and derivatives thereof are known for their desquamating properties (see WO-A-93/10756 and U.S. Pat. No. 4,767,750).
All of these compounds elicit an action against aging of the skin by promoting desquamation, namely, the removal of the "dead" cells located at the surface of the horny layer of the epidermis. This "desquamating" property is also referred to, often erroneously, as a keratolytic property.
However, the compounds of the prior art elicit side effects which include stinging, tightness, heating (or burning) and redness, which are unpleasant to the user.
Serious need, thus, continues to exist for anti-aging agents which elicit an activity that is at least as effective as that of the compounds of the prior art, but which do not present their drawbacks.